Server Programming

This part is about extending the server functionality with
user-defined functions, data types, triggers, etc. These are
advanced topics which should probably be approached only after all
the other user documentation about PostgreSQL has
been understood. Later chapters in this part describe the server-side
programming languages available in the
PostgreSQL distribution as well as
general issues concerning server-side programming languages. It
is essential to read at least the earlier sections of section 5 Extending SQL (covering functions) before diving into the
material about server-side programming languages.